1. Field of the Invention
This invention relates to an apparatus for driving an optical disc having multiple recording layers. In addition, this invention relates to a method of deciding optimum recording powers of a laser beam applied to an optical disc having multiple recording layers.
2. Description of the Related Art
There are DVDs (digital versatile discs) of various types such as a DVD-R (DVD-recordable), a DVD-RW (DVD-rewritable), and a DVD-RAM. Some DVDs each have a single recording layer while other DVDs each have multiple recording layers.
A two-layer single-sided DVD is an example of the multi-layer DVDs. The two-layer single-sided DVD has a disc substrate whose one side is formed with a laminate of two recording layers. The two recording layers can be optically accessed by a laser beam from one side of the DVD.
Regarding a typical single-layer DVD, optimum power control (OPC) is implemented as follows. To record a signal on the DVD, a recording laser beam modulated in accordance with the signal is applied to the DVD. The quality of the recorded signal on the DVD depends on the power of the recording laser beam applied thereto. The recording layer of the DVD has a power calibration area (PCA). Test recording and reproduction are performed on the DVD before a desired information signal is recorded thereon. During a first stage of the test recording and reproduction, test signals are sequentially recorded on the PCA in the DVD while the power of the recording laser beam is changed among different values. The test signals are assigned to the different powers of the recording laser beam, respectively. During a second stage of the test recording and reproduction, the recorded test signals are reproduced, and the reproduced test signals are evaluated. An optimum power of the recording laser beam is decided on the basis of the results of the evaluation of the reproduced test signals. During the recording of a desired information signal on the DVD which follows the test recording and reproduction, the recording laser beam is controlled at the decided optimum power.
Japanese patent application publication number 11-3550/1999 discloses an apparatus for recording and reproducing information on and from an optical disc having multiple recording layers. In the apparatus of Japanese application 11-3550, a reference recording layer is selected from the multiple recording layers. The non-selected recording layers are called the non-reference recording layers. Test signals each corresponding to a succession of shortest marks are sequentially recorded on a first prescribed radial position in the reference recording layer while the power of a recording laser beam is changed among different values. The test signals are assigned to the different powers of the recording laser beam, respectively. Thereafter, the recorded test signals are reproduced, and the greatest-amplitude one is selected from the reproduced test signals. The recording laser beam power corresponding to the greatest-amplitude reproduced test signal is used as an optimum power of the recording laser beam for the first prescribed radial position in the reference recording layer. Similarly, an optimum power of the recording laser beam is decided for each of second and later prescribed radial positions in the reference recording layer. Furthermore, an optimum power of the recording laser beam is decided for one of the prescribed radial positions in each of the non-reference recording layers. The ratio between the optimum power for the instant prescribed radial position in each of the non-reference recording layers and that for the instant prescribed radial position in the reference recording layer is set as a sensitivity coefficient. Optimum powers of the recording laser beam for the other prescribed radial positions in each of the non-reference recording layers are calculated by multiplying the sensitivity coefficient and the optimum powers for those prescribed radial positions in the reference recording layer.
Japanese patent application publication number 2000-311346 discloses first and second optical discs of different types respectively. The first optical disc has multiple recording layers. Each of the recording layers in the first optical disc has a data area and a trial write area. The second optical disc has multiple recording layers designed so that specified one of the recording layers has both a data area and a trial write area while the other recording layers have data areas only.
Japanese application 2000-311346 also discloses a first apparatus for recording and reproducing information on and from the first optical disc. In the case where information is required to be recorded on selected one of the recording layers of the optical disc, the first apparatus implements trial writing as follows. Test signals are sequentially recorded on the trial write area in the selected recording layer while the power of the recording laser beam is changed among different values. The recorded test signals are reproduced, and the reproduced test signals are compared. An optimum power of the recording laser beam for the selected recording layer is decided on the basis of the result of the comparison.
Japanese application 2000-311346 further discloses a second apparatus for recording and reproducing information on and from the second optical disc. In the case where information is required to be recorded on a recording layer other than the specified one, the second apparatus implements trial writing similarly to the above-mentioned case to decide an optimum recording laser power for the specified recording layer. Then, an optimum recording laser power for the present recording layer (the non-specified recording layer) is calculated from the decided optimum recording laser power for the specified recording layer in response to a predetermined coefficient.
In a two-layer single-sided DVD, the near recording layer is semitransparent while the far recording layer is reflective. During the recording of a signal on the near recording layer, a laser beam is focused thereon. During the recording of a signal on the far recording layer, the recording laser beam is applied thereto through the near recording layer. The application of the recording laser beam to the near recording layer to record a signal thereon changes the physical characteristics (for example, the refractive index and the shape) of the near recording layer from the original. Therefore, during the recording of a signal on the far recording layer, the intensity of the recording laser beam reaching the far recording layer depends on whether or not a portion of the near recording layer through which the recording laser beam passes has undergone signal recording. This fact makes it difficult to accurately decide an optimum power of the recording laser beam for the far recording layer. The previously-mentioned apparatus of Japanese application 11-3550 has a similar problem since the test signals are recorded on the reference recording layer and the non-reference recording layers at the same radial position.
The previously-mentioned first and second apparatuses of Japanese application 2000-311346 have problems as follows.
In the first apparatus of Japanese application 2000-311346, each time information is required to be recorded on selected one of the recording layers of the optical disc, the recording and reproduction of the test signals on and from the trial write area in the selected recording layer is always performed. Therefore, it tends to take a long time to decide an optimum recording laser power for the selected recording layer.
In the second apparatus of Japanese application 2000-311346, an optimum recording laser power for the non-specified recording layer is calculated without performing the recording and reproduction of the test signals on and from the non-specified recording layer. Therefore, the obtained optimum recording laser power for the non-specified recording layer tends to be low in accuracy.